Add plus and minus buttons for temperature, speed and extrusion.

I love the duet wifi and once I got it up and running properly (finally) I started to notice a few things that are missing in the web interface and I would love for them to be there. The thing I would like to see the most would be simple plus and minus buttons for increasing/decreasing temperature and the same for speed and extrusion. This would be very useful on the temperatures because you can adjust it on the fly without the need to go into the system properties and add temperatures to the list (this is kind of limiting as you have to add a new temperature every time you want to experiment). These would also be neat on the speed and extrusion sliders so that you can fine tune.